1. Field of the Invention
The present invention relates to a platen roller for conveying a thermally active adhesive sheet having a thermally active adhesive layer on a back-surface side of a recording surface of a sheet-like substrate, and a recording device, a thermal activation device, and a sticking label printer which are provided with the platen rollers.
2. Description of the Related Art
Heretofore, in many cases, a sticking label such as a POS label for foods, a physical distribution and delivery label, a medical label, a baggage tag, and a display label for bottles and cans is supplied in a tentatively bonded state in which a pressure-sensitive adhesive layer is disposed on a backside of a recording surface (printing surface), and separate paper (separator) is attached onto the layer. Moreover, after printing a predetermined barcode, price or the like on the recording surface, the sticking label is peeled from the separate paper, and attached for use. However, after this type of sticking label is used, the separate paper remains, and there is a problem that a waste is generated.
To solve the problem, there has been investigated utilization of a thermally active adhesive sheet having a thermally active adhesive layer on a backside, of a recording surface of a sheet-like substrate as the sticking label which does not generate any waste after use. The thermally active adhesive layer is formed of a material which does not have any adhesive property approximately at room temperature but which is thermally activated to develop the adhesive property when heated at, for example, about 50 to 150° C. The material forming the thermally active adhesive layer is constituted of a heat-sensitive adhesive material containing main components such as a thermoplastic resin and a solid plasticizer as disclosed in, for example, Patent Documents (Japanese Patent Application Laid-Open No. 10-140117, Japanese Patent Application Laid-Open No. 2002-105414, Japanese Patent Application Laid-Open No. 2002-114953, Japanese Patent Application Laid-Open No. 2002-114954, Japanese Patent Application Laid-Open No. 2002-114955, Japanese Patent Application Laid-Open No. 11-79152). When the solid plasticizer is heated and molten, the adhesive property is imparted to the thermoplastic resin. Since the molten solid plasticizer is brought into an overcooled state and gradually crystallized, the adhesive property is sustained for a predetermined time. While the sticking label has this adhesive property, the label can be attached to an object such as a glass bottle.
As thermal activation means for thermally activating the thermally active adhesive layer of such thermally active adhesive sheet, there are considered applications of various heating systems such as a system using a heating roll, a hot air spraying system, an infrared radiation system, and a system using an electrothermal heater or a dielectric coil. In Patent Document 6, there is disclosed a technology in which a thermal head is used as the thermal activation means. The thermal head is broadly utilized as a recording thermal head of a thermal printer, and has a plurality of resistors (heating elements) disposed on a ceramic substrate as heat sources. The thermal head is brought into contact with the thermally active adhesive layer of the thermally active adhesive sheet to heat the layer.
Here, FIG. 1 shows a schematic diagram of a general constitution of an adhesive or sticking label printer in which the thermal head is used as recording means for recording information on a recording surface and thermal activation means for thermally activating the thermally active means for thermally activating the thermally active adhesive layer. This sticking label printer is provided with a recording device 1, a thermal activation device 2, and a cutter unit 3. Moreover, when a thermally active adhesive sheet 4 wound into a roll shape is introduced into this sticking label printer, predetermined recording is performed on the recording surface of the thermally active adhesive sheet 4 by means of a recording thermal head 11 of the recording device 1, the thermally active adhesive sheet 4 is cut into an appropriate size by the cutter unit 3, the thermally active adhesive layer of the thermally active adhesive sheet 4 is thermally activated by a thermally activating thermal head 21 of the thermal activation device 2, and a targeted sticking label is discharged. This series of treatment is performed while the thermally active adhesive sheet 4 is conveyed by rollers such as appropriately disposed platen rollers. A dimethyl silicone rubber having a low compressive permanent set property is generally used as a material forming a roller portion of the platen roller.
However, in a case where the thermally active adhesive sheet is subjected to the recording and the thermal activating by the above-described sticking label printer, an adhesive force of the thermally active adhesive layer of the discharged thermally active adhesive sheet weakens or disappears depending on a place. The platen roller for use in the above-described sticking label printer deteriorates fast, and needs to be changed with a high frequency.